MORTEX
PRODUCTS
INC
501
TERMINAL
RD
FORT
WORTH,
TX
76106
Page
8
SECTION III: FURNACE DUCT CONNECTIONS AND
DUCT SYSTEM
General Information
1.
The duct system’s design and installation must handle an air
volume appropriate for the space being heated and must allow
the furnace to operate within the rating plate specifications.
2.
The duct system’s design and installation must be in
accordance with the NFPA standards pamphlets 90A and 90B
(latest editions) or applicable national, provincial, state, local
fire, and safety codes.
3.
The duct system’s design and installation must create a closed
duct system. Manufactured (Mobile) Home or Modular Home
installations. The furnace must be installed so the supply ducts
carry air circulated by the furnace to areas outside the space
containing the furnace. The return air is handled with a
louvered filter door attached to the furnace casing. The return
air duct(s) are not required by the manufacturer providing the
combustion air and vent system have been installed and
maintained as a two (2) pipe sealed combustion configuration
and provided the return air duct system is not required by state,
local, provincial, or regional codes.
4.
The duct systems design and installation must consist of a
properly sized duct system that provides a complete path for
heated or cooled air to circulate through the air conditioning
and heating equipment and to and from the conditioned space.
When the furnace is used in conjunction with a cooling coil, the coil
must be installed parallel with, or in the supply air side of the
furnace to avoid condensation in the primary heat exchanger. When
a parallel flow arrangement is used, dampers or other means used to
control air flow must be adequate to prevent chilled air from
entering the furnace. If manually operated, the damper must be
equipped with means to prevent the furnace or the air conditioner
from operating unless damper is full heating or full cooling position.
Figure 2: Duct Connector Dimensions
Floor Base Installation and Duct Connection
Downflow combustible floor base is used for installations on
combustible material or floors. The combustible floor base is
recommended by not required because the furnace base is insulated.
The combustible floor base is shown in Figure 3. Follow the
instructions supplied with the combustible floor base accessory to
be sure it is properly installed.
Figure 3: Duct Connector and Floor Base Installation
Downflow Duct Connectors
All downflow installations must use a suitable duct connector
approved by the furnace manufacturer for use with this furnace.
The duct connectors are designed as a transition between the
furnace base and the rectangular duct system under the floor. Refer
to the instructions supplied with the duct connector for proper
installation. The duct connector part number can be found in the
“Accessory Parts List” located in the Users Information Manual /
Service and Maintenance Manual.
When replacing an existing furnace the duct connector must be
checked to determine if the furnace will properly fit the duct
connector so all of the holes in the furnace base line up with the
holes in the duct connector. If the holes do not line up then, the duct
connector must be replaced.
The duct system is a very important part of the installation. If the
duct system is improperly sized the furnace will not operate
The cooling coil must be installed in the coil cabinet, or
in the supply air duct, downstream of the heat exchanger.
Cooled air may not be passed over the heat exchanger.
The duct system must be properly sized to obtain the
correct airflow for the furnace size that is being installed.
Refer to the furnace rating plate for the correct rise and
static pressures.
If the ducts are undersized, the result will be high duct
static pressure, and/or high temperature rises which can
result in a heat exchanger
overheating
condition. This
condition can result in premature heat exchanger failure,
which can result in personal injury, property damage, or
death.
